The only example I have met with of the phenomenon of anything like a complete intergradation between local types really distinct in kind is that provided by the butterfly _Pararge egeria_. It is well known to entomologists that this insect exists in two very different types, a northern one, the "Speckled Wood" of England, in which the spots are a pale whitish yellow, and a southern type having the full fulvous colour that we know as characteristic of _megaera_, the "Gatekeeper." It appears that Linnaeus gave the name _egeria_ to the southern type,[1] and our own is now called _egerides_. Broadly speaking, so far as Great Britain, France, and the Spanish Peninsula are concerned, the tawny-coloured _egeria_ occupies Spain and western France up to the latitude of Poitiers and the pale yellow _egerides_ extends from Scotland, where it has a scanty distribution, through southern England, where in suitable localities it is common, and the north of France to Paris.[2] The two types when placed side by side are strikingly different from each other, and are an excellent illustration of what is meant by climatic variation. The insect is not a great traveller and probably scarcely ever wanders far from its home. It should therefore be possible by collecting from north to south to find out how the transition is effected, whether suddenly or gradually. This at various times I have endeavoured to do, but I am still without exact information as to the population in certain critical areas. In addition to the information derived from specimens which I have collected or seen in the collections of others there is a good account of the general distribution in Europe given by the Speyers,[3] who evidently paid more attention to the subject than most lepidopterists have done, and many more recent records. In particular Oberthür[4] has published many details as to the distribution in western France and I am especially indebted to Mr. H. Rowland-Brown for a long series of notes as to the distribution in France generally, and to Mr. H. E. Page and Dr. T. A. Chapman, Mr. Oberthür Prof. Arrigoni degli Oddi, Mr. H. Williams and other correspondents, for showing me forms from many localities. The butterfly is attached for the most part to woods of deciduous trees and to country abounding in tall hedges or rough scrub. It is not usually to be found in highly cultivated districts or in very dry regions. Hence there is necessarily some want of continuity in the distribution at the present time and I should think a mile or two of arable land without big hedges would constitute a barrier hardly ever passed. The larva feeds on several coarse grasses, especially _Dactylis glomerata_. Barrett mentions also _Triticum repens_. In this country the winter is usually passed in the larval stage, but I have found that in captivity, at least, there is much irregularity. The larvæ feed whenever the weather is not very cold and may pupate, but if sharp cold comes on when they